1. Field of the Invention
The present invention generally relates to image processing apparatuses and image processing methods, and particularly to a technology for blurring an image.
2. Description of the Related Art
Digital products such as computers and digital television sets have been improved greatly over the years and they have now become very common. Digital image acquiring equipment such as digital cameras and digital video cameras is now so widespread that they seem almost certain to replace the conventional film cameras.
Images acquired using a digital camera or the like can be directly displayed on a digital device such as a computer, a digital television set, or a cellular phone, in addition to being printed on paper, thus providing greater joy to the people's lives. Also, image processing technologies that were originally developed for specialized purposes, such as medical devices, remote sensing devices, and communications devices, are increasingly affecting the people's daily lives. As of now, the state-of-the-art digital cameras already have resolution in excess of one million pixels.
When a conventional film camera is used, the parameters of the camera can be controlled to adjust the depth of field in order to obtain a photograph with a clear foreground and a blurred background. For example, when taking a picture of a person, the lens is precisely focused at the eye of the photographed person in accordance with the principle of imaging. As a result, the background of the person does not become clear due to the difference in object distance. When someone views the photograph, he or she does not notice the blurred background and instead immediately focuses their eyes on the clearest foreground. This is how a good personal photograph is taken.
Because the size of the CCD (charge coupled device) in digital cameras is smaller than the film, the digital cameras have greater depths of field. This means that, when a far object is photographed with a digital camera, it is harder to obtain the effect of the enhanced foreground and the blurred background or unwanted portions in a scene. In order to reproduce the background blurring function of the conventional film cameras, an experienced photographer may utilize image processing software. The work involved, however, takes a long time, and the finish varies depending on the experience level of the photographer.
The conventional art offers several methods for realizing the background blurring function. For example, a single frame of basic image is selected from a sequence of images, and a background region and a foreground region are generated using the other images. By blurring the background region, an image with the blurred background can be generated. In another example, an image having a high dynamic range is generated using two images with different exposure values, and the background of the generated image is blurred.
The image blurring technique can be used to enhance a baseball game scene, for example, in order to improve the effects of the game. In this case, the blurred area may be finalized depending on changes in the scene. Several overlays may be stored in memory in advance, so that an overlay and a photograph can be merged to obtain a blurred image.
In any of the aforementioned existing methods, plural images are used for realizing image blurring. However, use of plural images is associated with the problem of image registration, the accuracy of which directly influencing the generated image effect. In addition, it is sometimes difficult to obtain two images with exactly identical scenes.